Photocatalytic Reduction of CO2 with N-Doped TiO2-Based Photocatalysts Obtained in One-Pot Supercritical Synthesis

Abstract

The objective of this work was to analyze the effect of carbon support on the activity and selectivity of N-doped TiO2 nanoparticles. Thus, N-doped TiO2 and two types of composites, N-doped TiO2/CNT and N-doped TiO2/rGO, were prepared by a new environmentally friendly one-pot method. CNT and rGO were used as supports, triethylamine and urea as N doping agents, and titanium (IV) tetraisopropoxide and ethanol as Ti precursor and hydrolysis agent, respectively. The as-prepared photocatalysts exhibited enhanced photocatalytic performance compared to TiO2 P25 commercial catalyst during the photoreduction of CO2 with water vapor. It was imputed to the synergistic effect of N doping (reduction of semiconductor band gap energy) and carbon support (enlarging e−-h+ recombination time). The activity and selectivity of catalysts varied depending on the investigated material. Thus, whereas N-doped TiO2 nanoparticles led to a gaseous mixture, where CH4 formed the majority compared to CO, N-doped TiO2/CNT and N-doped TiO2/rGO composites almost exclusively generated CO. Regarding the activity of the catalysts, the highest production rates of CO (8 µmol/gTiO2/h) and CH4 (4 µmol/gTiO2/h) were achieved with composite N1/TiO2/rGO and N1/TiO2 nanoparticles, respectively, where superscript represents the ratio mg N/g TiO2. These rates are four times and almost forty times higher than the CO and CH4 production rates observed with commercial TiO2 P25.

Alkanolamine-Grafted and Copper-Doped Titanium Dioxide Nanosheets–Graphene Composite Heterostructure for CO2 Photoreduction

“…The catalysts produced methane and CO at 1.5 and 3.5, 0.2 and 0.75, and 0.1 and 3.9 μmol/g CAT /h, respectively. 34 Zhang and coworkers used the aluminothermic reduction method in synthesizing a black TiO 2 nanosheet array. The array was rich in oxygen vacancy sites for CO 2 photoreduction in an aqueous solution, generating methane and CO gases at 3.6 and 128.5 μmol/g CAT /h.…”

“…Pristine TNS shows a reflective peak at 420 nm, while MEA–TNS, DEA–TNS, and TEA–TNS display a peak at 440, 440, and 450 nm, respectively. The red shift in the light reflectance peak indicates an improvement in visible light absorption of the photocatalysts due to alkanolamine modification on TNS. ,, Optical bandgaps were determined by plugging the Kubelka–Munk function ( F ( R ), eq ) into the Tauc’s correlation (eq ), where R is the reflectance, h is the Planck constant, ν is the frequency of photons, B is a constant, and E g is bandgap energy. The power of the left-hand-side term is held at 1/2 for an indirect transition mode of electron transfer. …”

Pt–Cu@Bi2MoO6/TiO2 Photocatalyst for CO2 Reduction

“…However, the high recombination rate of photogenerated electron–hole pairs, limited CO 2 adsorption capacity, and wide band gap are the main limitations of the TiO 2 photocatalyst . To overcome these limitations, various methods like morphology control, , impurity doping, − hybridization, and composite construction − have been employed to enhance visible light absorption capacity, limit the recombination rate of photoinduced electron–hole pairs, and thus enhance the photocatalytic activity in the visible light region. , Among these methods, coupling TiO 2 with other semiconductors with a narrow band gap leads to the formation of a heterojunction that has attracted attention due to the low recombination rate of electron–hole pairs and enhanced visible light absorption. − Bi-based semiconductors with narrow band gaps are a good candidate for combining with TiO 2 to form a heterojunction. − Bi doping was reported to enhance the CO 2 adsorption capacity of TiO 2 photocatalysts due to the oxygen vacancy formation . Combining of TiO 2 with Bi-based semiconductors is an effective strategy to improve the photocatalytic activity because the advantages of each component can be combined in composite photocatalysts .…”

Nitrogen-Doped TiO2/Nitrogen-Containing Biochar Composite Catalyst as a Photocatalytic Material for the Decontamination of Aqueous Organic Pollutants

“…The nonmetal-doped TiO 2 will form new impurity energy levels above the valence bond band, which reduces the band gap and promotes the red-shift of the absorption edge. − That means that the doped TiO 2 can obtain significant photocatalytic activity under visible-light irradiation. For instance, Chen et al found that the nitrogen-doped method could result in the enhancement of visible-light absorption and the generation of photoinduced surface oxygen vacancies.…”